Linear compressor

ABSTRACT

Disclosed herein is a linear compressor. The linear compressor comprises a cylinder provided at one side thereof with an outlet part, and a piston reciprocated in the cylinder by means of a liner motor for compressing a fluid. The piston has a fluid flow channel formed therethrough. The fluid flow channel communicates with the interior of the cylinder. To the rear part of the piston is fixedly attached a first muffler so that the first muffler is linearly moved along with the piston. The first muffler has a fluid flow channel formed therein. The fluid flow channel of the first muffler communicates with the fluid flow channel of the piston. The first muffler also has a noise-reducing space defined therein. In the compressor is fixedly mounted a second muffler such that the inner volume of the second muffler is variable as the first muffler is linearly moved. The second muffler has a fluid flow channel formed therein. The fluid flow channel of the second muffler communicates with the fluid flow channel of the first muffler. The second muffler also has a noise-reducing space defined therein. According to the present invention, introduction efficiency of the linear compressor is improved, and noise generated at various bands is effectively reduced.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a linear compressor, and more particularly to a linear compressor that is capable of reducing noise and vibration generated in the course of compressing a fluid and improving compression efficiency.

[0003] 2. Description of the Related Art

[0004] Generally, a linear compressor is constructed such that a linear driving force from a linear motor is transmitted to a piston, which is linearly reciprocated in a cylinder, whereby a fluid is introduced and compressed.

[0005]FIG. 1 is a longitudinal sectional view showing a conventional linear compressor.

[0006] As shown in FIG. 1, the conventional linear compressor includes an inner case 10 mounted inside a hermetically sealed container 1. The inner case 10 is formed in the shape of a cylinder having a prescribed length. To one side of the inner case 10 is fixed a back cover 20 having a fluid inlet channel 18 formed therein. Inside the inner case 10 is mounted a driving motor 30 for generating a driving force.

[0007] To the driving motor 30 is connected a piston 40 having a fluid flow channel 38 formed therein. To the piston 40 is attached an inlet valve 50 for opening and closing the fluid flow channel 38. To the other side of the inner case 10 is fixed a cylinder block 60 having a cylinder 58, in which the piston 40 is movably fitted such that the piston 40 can be moved forward and backward in the cylinder 58. To the cylinder block 60 is attached an outlet valve 70 for opening and closing the cylinder 58.

[0008] To the hermetically sealed container 1 is connected an inlet connection pipe 2, through which a fluid is introduced into the hermetically sealed container 1 from the outside, in such a manner that the inlet connection pipe 2 is disposed in the rear of the fluid inlet channel 18 of the back cover 20.

[0009] The driving motor 30 includes: a stator S comprising an outer cylindrical laminated core 31, an inner cylindrical laminated core 32 disposed such that the inner core 32 is spaced apart from the outer core 31 by a prescribed gap distance, and a coil 33 wound on the outer core 31; a magnet 34 disposed such that the magnet 34 is moved forward/backward between the outer core 31 and the inner core 32; and a magnet frame 36 connected to the piston 40 so that the piston 40 is moved forward/backward when the magnet 34 is moved forward/backward. The magnet 34 is fixed to the magnet frame 36.

[0010] The outer core 31 is fixedly attached to the back cover 20 in the inner case 10. The inner core 32 is fixedly attached to a cylindrical connection part 21 formed at the back cover 20. The magnet 34 is fixed to the outer circumference of the magnet frame 36 while being disposed between the outer core 31 and the inner core 32.

[0011] The magnet frame 36 is elastically supported by means of a first spring 37 a disposed between the magnet frame 36 and the cylinder block 60. The piston 40 is elastically supported by means of a second spring 37 b disposed between the piston 40 and the inner core 32.

[0012] The inlet valve 50 is a plate valve wherein one side of the plate valve is fixed to the piston 40, and the part of the plate valve for opening and closing the fluid flow channel 38 of the piston 40 is elastically bent.

[0013] Consequently, when the piston 40 is moved backward toward the back cover 120, the part of the inlet valve 50 for opening and closing the fluid flow channel 38 of the piston 40 is bent in the direction opposite to the back cover 20 by means of the fluid existing in the fluid flow channel 38, whereby the fluid flow channel 38 is opened. On the other hand, when the piston 40 is moved forward toward the-outlet valve 70, the part of the inlet valve 50 for opening and closing the fluid flow channel 38 of the piston 40 is straightened in the direction opposite to the outlet valve 70 by means of the fluid existing between the inlet valve 50 and the outlet valve 70 and by means of its own elastic force, whereby the fluid flow channel 38 is closed.

[0014] The outlet valve 70 comprises: an outlet cover 72 mounted to the cylinder block 60 and connected to an outlet pipe at one side thereof; and a valve body 76 supported against the outlet valve 72 by means of a spring 74 and disposed such that the valve body 76 makes close contact with the end of the cylinder 58 for opening and closing the cylinder 58.

[0015] In the above-mentioned linear compressor, the inlet valve 50 is dashed against the piston 40 when the inlet valve 50 is opened and closed, whereby noise is generated. Also, the valve body 76 is dashed against the cylinder 58 when the outlet valve 70 is opened and closed, whereby noise is generated. Such noise is transmitted to the outside of the hermetically sealed container 1 through the fluid flow channel 38 of the piston 40, a fluid flow hole of the inner core 32, and the fluid inlet channel 18 of the back cover 20, as shown in FIG. 1.

[0016] For this reason, an additional muffler is mounted in such a noise-transmitting path for preventing the transmission of the noise to the outside of the hermetically sealed container 1.

[0017] The muffler 80 is fixedly attached to the rear part of the piston 40 while being spaced apart from the fluid inlet channel 18 of the back cover 20. The muffler 80 has fluid flow holes 82 longitudinally formed therethrough, through which the fluid introduced through the fluid inlet channel 18 of the back cover 20 is guided into the fluid flow channel 38 of the piston 40. The muffler 80 is constructed such that the diameter of the middle part of the fluid flow channel 82 is larger than that of the front and rear parts of the fluid flow channel 82.

[0018] The operation of the conventional linear compressor with the above-stated construction will now be described.

[0019] When electric current is supplied to the coil 33, the driving motor 30 is operated so that the magnet 34 is linearly reciprocated. The reciprocating movement of the magnet 34 is transmitted to the piston 40 via the magnet frame 36. As a result, the piston 40 is linearly reciprocated in the cylinder 58.

[0020] As the piston 40 is linearly reciprocated On the cylinder 41, the outlet valve 70 and the inlet valve 50 are opened and closed. At this time, the gaseous fluid introduced into the hermetically sealed container 1 is guided into the cylinder 58 through the fluid inlet channel 18 of the back cover 20, the fluid flow channel of the inner core 32, the muffler 80, and the fluid flow channel 38 of the piston 40. In the cylinder 58, the gaseous fluid is compressed and then discharged. The discharged high-temperature and high-pressure fluid gas is discharged to the outside of the hermetically sealed container 1 through a discharging pipe (not shown).

[0021] In the above-mentioned conventional linear compressor, however, the muffler 80 is reciprocated along with the piston 40 while being spaced apart from the fluid inlet channel 18 of the back cover 20. As a result, the fluid introduced through the fluid inlet channel 18 of the back cover 20 is not quickly guided into the fluid flow channel 38 of the cylinder through the muffler 80 as indicated by the solid line in FIG. 1. Consequently, introduction efficiency of the linear compressor is decreased, and thus performance of the linear compressor is decreased.

SUMMARY OF THE INVENTION

[0022] Therefore, the present invention has been made in view of the above problems, and it is an object of the present invention to provide a linear compressor including a muffler the volume of which is variable as a piston is reciprocated, whereby introduction efficiency of the linear compressor is improved, and noise generated at various bands is effectively reduced.

[0023] In accordance with one aspect of the present invention, the above and other objects can be accomplished by the provision of a linear compressor comprising: a cylinder provided at one side thereof with an outlet part; a piston reciprocated in the cylinder by means of a liner motor for compressing a fluid, the piston having a fluid flow channel formed therethrough, the fluid flow channel communicating with the interior of the cylinder; a first muffler fixedly attached to the rear part of the piston so that the first muffler is linearly moved along with the piston, the first muffler having a fluid flow channel formed therein, the fluid flow channel of the first muffler communicating with the fluid flow channel of the piston, the first muffler also having a noise-reducing space defined therein; and a second muffler fixedly mounted in the compressor such that the inner volume of the second muffler is variable as the first muffler is linearly moved, the second muffler having a fluid flow channel formed therein, the fluid flow channel of the second muffler communicating with the fluid flow channel of the first muffler, the second muffler also having a noise-reducing space defined therein.

[0024] Preferably, the first muffler is constructed so that the rear part of the first muffler is reciprocated while being inserted in the second muffler.

[0025] Preferably, the gap distance between the outer circumferential surface of the first muffler and the inner circumferential surface of the second muffler is 0.1 to 1.0 mm.

[0026] Preferably, the first muffler is formed in the shape of a cylinder having fluid flow holes formed through the front and rear parts thereof, respectively, so that the fluid passes through the fluid flow holes.

[0027] Preferably, the second muffler is formed in the shape of a cylinder, the cylinder being opened at the front part thereof so that the first muffler is inserted into the second muffler, the cylinder having an inlet hole formed therethrough so that the fluid is introduced through the inlet hole.

[0028] Preferably, the first muffler is provided with a Helmholtz resonator, and the Helmholtz resonator has a space formed at the inner circumference of the first muffler in the circumferential direction.

[0029] Preferably, at least one of the first muffler and the second muffler has a collection space internally formed at the rear part thereof.

[0030] Preferably, the collection space is formed in the vicinity of an inlet pipe where the hole of the first muffler or the second muffler is extended toward the interior of the muffler. The inlet pipe is gradually expanded toward the rear part thereof.

[0031] Preferably, the compressor further comprises a back cover fixed to the rear part of the linear motor, the back cover having an opening formed at the center part thereof, wherein the second muffler is fixedly fitted in the opening of the back cover.

[0032] Preferably, at least one of the first and second mufflers is made of a non-magnetic material.

[0033] The present invention provides a linear compressor having a muffler, the inner volume of which is variable as a piston is reciprocated. Consequently, the present invention has an effect of interrupting noise generated at various bands in the variable space of the muffler with the result that the high-frequency component of the noise is effectively reduced.

[0034] Also, the linear compressor according to the present invention includes an inlet channel, which comprises a first muffler and a second muffler, formed between a back cover and a piston. Consequently, leakage of a fluid from the first and second mufflers, the piston, and the cylinder is minimized. Furthermore, the second muffler serves to pump the fluid as the volume of the second muffler is varied, whereby the amount of the fluid introduced into the cylinder is increased, and thus introduction efficiency of the linear compressor is improved.

BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

[0036]FIG. 1 is a longitudinal sectional view showing a conventional linear compressor;

[0037]FIG. 2 is a longitudinal sectional view showing a linear compressor according to a preferred embodiment of the present invention;

[0038]FIG. 3 is a sectional view of the linear compressor according to the preferred embodiment of the present invention showing the operation of the linear compressor when a piston is moved forward;

[0039]FIG. 4 is a sectional view of the linear compressor according to the preferred embodiment of the present invention showing the operation of the linear compressor when a piston is moved backward;

[0040]FIG. 5 is a sectional view of a linear compressor according to another preferred embodiment of the present invention showing main components of the linear compressor; and

[0041]FIG. 6 is a sectional view of a linear compressor according to still another preferred embodiment of the present invention showing main components of the linear compressor.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0042] Now, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0043] It should be understood that linear compressors according to numerous preferred embodiments of the present invention may be proposed, although only the most preferred embodiments of the present invention will be hereinafter described.

[0044]FIG. 2 is a longitudinal sectional view showing a linear compressor according to a preferred embodiment of the present invention.

[0045] As shown in FIG. 2, the linear compressor according to the present invention includes: a hermetically sealed container 104 comprising a lower container 101 and an upper cover 104; a cylinder block 110 placed on a first damper 106 mounted to one side of the hermetically sealed container 104 in such a manner that shock applied to the cylinder block 110 is absorbed by means of the first damper 106, the cylinder block 110 having a cylinder 109 formed therein; a back cover 120 placed on a second damper 108 mounted to the other side of the hermetically sealed container 104 in such a manner that shock applied to the back cover 120 is absorbed by means of the second damper 108, the back cover 120 being spaced apart from the cylinder 109 and the cylinder block 110; a linear motor 130 fixedly disposed between the cylinder block 110 and the back cover 120 for generating a driving force, which is required to compress the fluid; a piston 144 connected to the linear motor 130 so that the fluid in the cylinder 109 is compressed by means of the piston 144 as the piston 144 is reciprocated in the cylinder 109, the piston 144 having a fluid flow channel 140 formed therein, through which the fluid is introduced into the cylinder 109, the piston 144 being provided with an inlet valve 142 for opening and closing the fluid flow channel 140; an outlet valve 150 for opening and closing the outlet of the cylinder 109, the outlet valve 150 defining a compression chamber C together with the cylinder 109 and the piston 144; a first muffler 160 attached to the piston 144, the first muffler 160 having a communication hole 160 a formed therein, the communication hole 160 a communicating with the fluid flow channel 140 of the piston 144, the first muffler 160 having an inlet hole 160 b, through which the fluid is introduced, the first muffler 160 also having a noise-reducing space defined therein; and a second muffler 170 attached to the back cover 120 is such a manner that the inner volume of the second muffler 170 is variable as the first muffler 160 is moved forward/backward, the second muffler 170 having an inlet hole 170 a communicating to the outside of the back cover 120 so that a fluid outside the back cover 120 is introduced through the inlet hole 170 a.

[0046] To the rear part of the hermetically sealed container 104 is connected an inlet connection pipe 104 a in such a manner that the inlet connection pipe 104 a is penetrated into the hermetically sealed container 104. Below the inlet connection pipe 104 a is disposed an outlet connection pipe 104 b for discharging the compressed fluid in such a manner that the outlet connection pipe 104 b is also penetrated into the hermetically sealed container 104.

[0047] The back cover 120 is provided with an opening 120 a, in which the second muffler 170 is fitted, so that the fluid in the hermetically sealed container 104 is directly introduced into the second muffler 170 through the inlet hole 170 a.

[0048] The opening 120 a of the back cover 120 is formed such that the opening 120 a is placed at the same level as the centers of the piston 144 and the first muffler 160. Preferably, the inner diameter of the opening 120 a of the back cover 120 is equal to or slightly larger than the outer diameter of the first muffler 160 so that the first muffler 160 is inserted in the opening 120 a of the back cover 120.

[0049] The linear motor 130 comprises a stator S and a mover M. The stator S comprises: an outer laminated core 131; an inner laminated core 132 disposed such that the inner core 132 is spaced apart from the outer core 131 by a prescribed gap distance; and a coil 133 wound on the outer core 131. The mover M comprises: a magnet 134 moving forward/backward by means of a magnetic force generated around the coil 133; and a magnet frame 136 disposed between the outer core 131 and the inner core 132 such that the magnet frame 136 moves forward/backward. The magnet 134 is fixed to the magnet frame 136. The magnet frame 136 is fixedly attached to the piston 144.

[0050] The outer core 131 is disposed between the cylinder block 110 and the back cover 120 while the outer core 131 is fixed to the cylinder block 110 and the back cover 120 by means of suitable fastening members. The inner core 132 is fixed to the cylinder block 110 by means of suitable fastening members. The magnet frame 136 is fixed to the piston 144 by means of suitable fastening members.

[0051] A portion of the piston 144 is inserted into the cylinder 109 while being reciprocated in the cylinder 109 so that the piston 144 moves forward and backward in the cylinder 109. To one side of the piston 144, which is inserted in the cylinder 109, is fixed the inlet valve 142, and at the other side of the piston 144, which is not inserted in the cylinder 109, is formed a fixing part 146 protruded in the radial direction. The fixing part 146 of the piston 144 is fixed to the magnet frame 136 by means of suitable fastening members.

[0052] The piston 144 is elastically supported by means of a first spring 144a disposed between one surface of the fixing part 146 and the cylinder block 110 and a second spring 144b disposed between the other surface of the fixing part 146 and the back cover 120 so that the piston 144 is reciprocated along with the mover M of the linear motor 130 and the first muffler 160.

[0053] Preferably, the inlet valve 142 may be a plate valve wherein one side of the plate valve is fixed to the piston 144, and the part of the plate valve corresponding to the fluid flow channel 140 of the piston 144 is elastically bent.

[0054] The outlet valve 150 comprises: an inner outlet cover 152 mounted to the cylinder block 110 while communicating with the first cylinder 109 and having a fluid outlet hole 151 formed at one side thereof; an outer outlet cover 154 disposed outside the inner outlet cover 152 while being spaced apart from the inner outlet cover 152, the outer outlet cover 154 being connected to a fluid outlet pipe 153 for discharging the fluid at one side thereof; and a valve body 158 elastically supported by means of a spring 156 disposed in the inner outlet cover 152 for opening or closing the first cylinder 109 as the valve body 158 makes contact with or withdraws from the end of the cylinder 109.

[0055] It is preferable that at least one of the first and second mufflers 160 and 170 is made of a non-magnetic material so that decrease of compression efficiency of the linear compressor is prevented.

[0056] Specifically, the linear motor 130 includes the coil 133 and the magnet 134, thereby generating a strong magnetic force. Most of components constituting the linear compressor are generally made of steel materials. If both of the first muffler 160 and the second muffler 170 are made of magnetic materials, the magnetic force generated by means of the linear motor 130 is transmitted to the second muffler 170 and the back cover 120 via the fist muffler 160. As a result, an electromagnetic loss is incurred. Furthermore, the forward/backward movement of the first muffler 160 is not smoothly carried out due to the magnetic force of the first muffler 160 and the second muffler 170.

[0057] The first muffler 160 is formed in the shape of a cylinder having a noise-reducing resonance space defined therein. The first muffler 160 is provided at the center part of one surface thereof, which is attached to the piston 144, with the communication hole 160 a. The first muffler 160 is also provided at the center part of the other surface thereof, which is moved into the second muffler 170, with the inlet hole 160 b.

[0058] The second muffler 170 is formed in the shape of a cylinder having a resonance space defined therein. The front part of the second muffler 170 is opened so that the rear part of the first muffler 160 is inserted into the second muffler 170. The second muffler 170 is provided at the center part of the rear surface thereof with the inlet hole 170 a. The resonance space of the second muffler 170 is variable by means of the first muffler 160, whereby noise generated at various bands is effectively reduced.

[0059] Reference numeral 200 indicates a loop pipe having one end connected to the fluid outlet pipe 153 and the other end connected to the outlet connection pipe 104 b.

[0060]FIG. 3 is a sectional view of the linear compressor according to the preferred embodiment of the present invention showing the operation of the linear compressor when a piston is moved forward, and FIG. 4 is a sectional view of the linear compressor according to the preferred embodiment of the present invention showing the operation of the linear compressor when a piston is moved backward.

[0061] The first muffler 160 includes at least one high frequency noise-reducing expansion chamber 162 or at least one low frequency noise-reducing Helmholtz resonator 164.

[0062] The expansion chamber 162 is formed at the inner front part of the first muffler 160 such that the expansion chamber 162 is extended in the longitudinal direction.

[0063] The Helmholtz resonator 164 is formed such that the Helmholtz resonator 164 has a space formed at the inner rear part of the first muffler 160 in the circumferential direction. The space of the Helmholtz resonator 164 communicates with the interior of the first muffler 160 through communication holes 163.

[0064] The second muffler 170 comprises: a rear part 172 disposed at the opening 120 a of the back cover 120, the rear part 172 having the inlet hole 170 a formed therethrough; and a cylindrical part 180 extended forward from the edge of the rear part 172 such that the cylindrical part 180 partially surrounds the circumference of the first muffler 160 to prevent leakage of the fluid.

[0065] Preferably, the gap distance t between the cylindrical part 180 partially surrounding the circumference of the first muffler 160, and the circumference of the first muffler 160 is 0.1 to 1.0 mm.

[0066] Specifically, it is preferable to set the gap distance t between the cylindrical part 180 and the first muffler 160 to 0.1 mm or more considering assembly tolerance of the cylindrical part 180 and the first muffler 160 or the forward/backward movement of the first muffler 160. If the gap distance t is too large, however, fluid leakage is increased. Therefore, it is preferable that the gap distance t be limited to 1.0 mm or less.

[0067] The operation of the linear compressor with the above-stated construction according to the present invention will now be described in detail.

[0068] When electric current is supplied to the coil 133 of the linear motor 130, there is created a magnetic field around the coil 133, and the magnet 134 is moved forward and backward due to the magnetic field created around the coil 133. The forward/backward movement of the magnet 134 is transmitted to the piston 144 and the first muffler 160 via the magnet frame 136.

[0069] The piston 144 is moved forward and backward in the cylinder 109 so that the interior of the compression chamber C is compressed by means of the first piston 144. The first muffler 160 is moved forward and backward in the second muffler 170 so that the inner volume of the second muffler 170 is varied by means of the first muffler 160. As the inner volume of the second muffler 170 is varied by means of the first muffler 160, noise generated at various bands is effectively reduced.

[0070] The inlet valve 142 and the outlet valve 150 are opened and closed due to change of the pressure caused by means of the forward/backward movement of the piston 144 and the first muffler 160, and the fluid (indicated by a solid line in FIGS. 3 and 4) is introduced into the hermetically sealed container 104 through the inlet connection pipe 104 a.

[0071] The fluid introduced into the hermetically sealed container 104 is guided to the interior of the second muffler 170 through the inlet hole 170 a of the second muffler 170. At this time, the fluid is guided along the cylindrical part 10 of the second muffler 170, whereby leakage of the fluid to the vicinity of the first muffler 160 is maximally prevented. Subsequently, the fluid is introduced into the first muffler 160 through the inlet hole 160 b of the first muffler 160.

[0072] The fluid introduced into the first muffler 160 passes through the communication hole 160 a of the first muffler 160, the fluid flow channel 140 of the piston 144, and the inlet valve 142 in turn, and is then introduced into the compression chamber C, where the fluid is compressed. The compressed fluid is discharged through the outlet valve 150, the outlet pipe 153, the loop pipe 200, and the outlet connection pipe 104 b in turn.

[0073] When the inlet valve and the outlet valve are opened and closed in the above-mentioned linear compressor according to the present invention, shock between the inlet valve and the outlet valve occurs, whereby noise is generated. Such noise is transmitted to the interior of the first muffler 160 through the fluid flow channel 140 of the piston 144 and the communication hole 160 a of the first muffler 160.

[0074] The noise transmitted to the interior of the: first muffler 160 passes through the Helmholtz resonator 164 so that the noise components at the low-frequency bands are interrupted. The noise components at the high-frequency bands, which have not been interrupted by means of the first muffler 160, are transmitted to the interior of the second muffler 170 so that the noise components at the high-frequency bands are interrupted.

[0075] The noise transmitted to the second muffler 170 is interrupted by means of the inner space of the second muffler 170. At this time, noise generated at various bands is effectively reduced as the inner volume of the second muffler 170 is varied. Consequently, the amount of the noise transmitted to the outside of the hermetically sealed container 104 through the second muffler 170 is minimized.

[0076]FIG. 5 is a sectional view of a linear compressor according to another preferred embodiment of the present invention showing main components of the linear compressor.

[0077] As shown in FIG. 5, the linear compressor according to the present invention includes an inlet pipe 174 extended toward the first muffler 160 so that a collection space for reducing noise is formed at the rear part 172 of the second muffler 170. The inner diameter of the inlet pipe 174 is gradually decreased toward the first muffler 160, in which an inlet hole 170 a is defined.

[0078] The first muffler 160 is provided with an inlet pipe 166 having the same or similar shape as the inlet pipe 174 of the second muffler 170 so that noise is collected by means of the first muffler 160 while not colliding with or interfering with the inlet pipe 174 of the second muffler 170. The inlet pipe 166 of the first muffler 160 has an inlet hole 160 b defined therein.

[0079] The linear compressor according to the second preferred embodiment of the present invention is identical to the compressor according to the previously described first preferred embodiment of the present invention in terms of construction and operation except that the construction of the first muffler and the second muffler according to the second preferred embodiment of the present invention is different from that according to the first preferred embodiment of the present invention. Therefore, elements of the linear compressor according to the second preferred embodiment of the present invention, which correspond to those of the linear compressor according to the first preferred embodiment of the present invention, are indicated by the same reference numerals as those of the linear compressor according to the first preferred embodiment of the present invention, and a detailed description thereof will not be given.

[0080] The inlet pipe 174 of the second muffler 170 is formed at the inner center part of the cylindrical part 180 such that the inlet pipe 174 is spaced apart from the inner circumferential surface of the cylindrical part 180 of the second muffler 170. The inlet pipe 174 of the second muffler 170 serves to carry out the same functions as the inlet part 166 of the first muffler 160.

[0081] Preferably, each of the inlet parts 166 and 174 is formed in the shape of a funnel, which is increasingly expanded toward the rear thereof so that the fluid is easily introduced.

[0082] Reference numeral 165 indicates a protruded pipe extended into the fluid flow channel 140 of the piston 144.

[0083]FIG. 6 is a sectional view of a linear compressor according to still another preferred embodiment of the present invention showing main components of the linear compressor.

[0084] In the linear compressor according to the present invention as shown in FIG. 6, the second muffler 170 is mounted in the back cover 120, and the back cover 120 has a communication hole 120 b, which communicates with the inlet hole 170 a of the second muffler 170, formed therethrough. Other constructions of the linear compressor according to the third preferred embodiment of the present invention are identical to those of the linear compressor according to the previously described first preferred embodiment of the present invention. Therefore, elements of the linear compressor according to the third preferred embodiment of the present invention, which correspond to those of the linear compressor according to the first preferred embodiment of the present invention, are indicated by the same reference numerals as those of the linear compressor according to the first preferred embodiment of the present invention, and a detailed description thereof will not be given.

[0085] Preferably, the size of the communication hole 120 b of the back cover 120 is equal to or slightly larger than that of the inlet hole 170 a of the second muffler 170. The fluid existing in the hermetically sealed container 104 is guided through the communication hole 120 b of the back cover 120 and the inlet hole 170 a of the second muffler 170 in turn.

[0086] It should be noted that the present invention is not limited to the above-mentioned embodiments. For example, the linear compressor according to the present invention may include a plurality of first muffler, each of which is moved forward/backward, and a plurality of second muffler, the inner volumes of which are variable by means of the first muffler, respectively.

[0087] As apparent from the above description, the present invention provides a linear compressor having a muffler, the inner volume of which is variable as a piston is reciprocated. Consequently, the present invention has an effect of interrupting noise generated at various bands in the variable space of the muffler with the result that high-frequency components of the noise are effectively reduced.

[0088] Also, the linear compressor according to the present invention includes an inlet channel, which comprises a first muffler and a second muffler, formed between a back cover and a piston. Consequently, fluid leakage from the first and second mufflers, the piston, and the cylinder is minimized. Furthermore, the second muffler serves to pump the fluid as the volume of the second muffler is varied, whereby the amount of the fluid introduced into the cylinder is increased, and thus introduction efficiency of the linear compressor is improved.

[0089] Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims. 

What is claimed is:
 1. A linear compressor comprising: a cylinder provided at one side thereof with an outlet part; a piston reciprocated in the cylinder by means of a liner motor for compressing a fluid, the piston having a fluid flow channel formed therethrough, the fluid flow channel communicating with the interior of the cylinder; a first muffler fixedly attached to the rear part of the piston so that the first muffler is linearly moved along with the piston, the first muffler having a fluid flow channel formed therein, the fluid flow channel of the first muffler communicating with the fluid flow channel of the piston, the first muffler also having a noise-reducing space defined therein; and a second muffler fixedly mounted in the compressor such that the inner volume of the second muffler is variable as the first muffler is linearly moved, the second muffler having a fluid flow channel formed therein, the fluid flow channel of the second muffler communicating with the fluid flow channel of the first muffler, the second muffler also having a noise-reducing space defined therein.
 2. The compressor as set forth in claim 1, wherein the first muffler is constructed so that the rear part of the first muffler is reciprocated while being inserted in the second muffler.
 3. The compressor as set forth in claim 2, wherein the gap distance between the outer circumferential surface of the first muffler and the inner circumferential surface of the second muffler is 0.1 to 1.0 mm.
 4. The compressor as set forth in claim 1, wherein the first muffler is formed in the shape of a cylinder having fluid flow holes formed through the front and rear parts thereof, respectively, so that the fluid passes through the fluid flow holes.
 5. The compressor as set forth in claim 1, wherein the second muffler is formed in the shape of a cylinder, the cylinder being opened at the front part thereof so that the first muffler is inserted into the second muffler, the cylinder having an inlet hole formed therethrough so that the fluid is introduced through the inlet hole.
 6. The compressor as set forth in claim 1, wherein the first muffler is provided with a Helmholtz resonator.
 7. The compressor as set forth in claim 6, wherein the Helmholtz resonator has a space formed at the inner circumference of the first muffler in the circumferential direction.
 8. The compressor as set forth in claim 1, wherein at least one of the first muffler and the second muffler has a collection space formed internally at the rear part thereof.
 9. The compressor as set forth in claim 8, wherein the collection space is formed in the vicinity of an inlet pipe where the hole of the first muffler or the second muffler is extended toward the interior of the muffler.
 10. The compressor as set forth in claim 9, wherein the inlet pipe is gradually expanded toward the rear part thereof.
 11. The compressor as set forth in claim 1, further comprising a back cover fixed to the rear part of the linear motor, the back cover having an opening formed at the center part thereof, wherein the second muffler is fixedly fitted in the opening of the back cover.
 12. The compressor as set forth in claim 1, wherein at least one of the first and second mufflers is made of a non-magnetic material.
 13. A linear compressor comprising: a cylinder provided with an outlet valve; a piston disposed such that the piston is moved forward/backward in the cylinder, the piston having a fluid flow channel formed therethrough so that a fluid is introduced into the interior of the cylinder through the fluid flow channel; a linear motor mounted in the compressor for reciprocating the piston; a back cover fixed to the linear motor such that the back cover surrounds the rear part of the piston, the back cover having an opening formed at the center part thereof; a first muffler fixedly attached to the rear part of the piston so that the first muffler is reciprocated along with the piston, the first muffler having an inlet hole formed therein so that a fluid is introduced into the first muffler through the inlet hole of the first muffler, the inlet hole of the first muffler communicating with the fluid flow channel of the piston; and a second muffler fixedly mounted to the back cover such that the inner volume of the second muffler is variable as the first muffler is reciprocated along with the piston, the second muffler having an inlet hole formed therein, the inlet hole of the second muffler communicating with the outside of the back cover so that the fluid existing outside the back cover is introduced into the second muffler through the inlet hole of the second muffler.
 14. The compressor as set forth in claim 13, wherein at least one of the first and second mufflers is made of a non-magnetic material.
 15. The compressor as set forth in claim 13, wherein the first muffler is constructed so that the rear part of the first muffler is linearly moved while being inserted in the second muffler.
 16. The compressor as set forth in claim 15, wherein the gap distance between the first muffler and the second muffler is 0.1 to 1.0 mm.
 17. The compressor as set forth in claim 13, wherein the first muffler is provided with a Helmholtz resonator.
 18. The compressor as set forth in claim 13, wherein at least one of the first muffler and the second muffler has a collection space formed internally at the rear part thereof.
 19. The compressor as set forth in claim 18, wherein the collection space is formed in the vicinity of an inlet pipe where the hole of the first muffler or the second muffler is extended toward the interior of the muffler.
 20. The compressor as set forth in claim 19, wherein the inlet pipe is gradually expanded toward the rear part thereof. 